Audi said 2.1 million cars worldwide were fitted with the software that allowed parent company, Volkswagen, to cheat emission tests.

Some 1.42 million Audi vehicles with so-called EU5 engines are affected in Western Europe, with 577,000 in Germany and almost 13,000 in the United States, a spokesman for Ingolstadt-based Audi said on Monday.

Affected model lines include the A1, A3, A4, A5, A6, TT, Q3 and Q5, the spokesman said.

VW said last week around 11 million cars of its group brands worldwide are affected by the diesel emissions scandal.

Additionally, Volkswagen has suspended the research and development chiefs of its core VW brand, luxury division Audi and sports-car maker Porsche, sources familiar with the matter said on Monday.

The carmaker's supervisory board last Friday agreed to put a number of employees on leave until the details of VW's emissions cheating scandal were cleared up, without providing names.

Reuters reported last Thursday that VW would fire top brand executives as it tries to recover from the scandal.

Audi, VW and Porsche declined comment.

Probe launched

German prosecutors have opened an investigation against former Volkswagen CEO Martin Winterkorn in the company's emissions-rigging scandal, Associated Press reports.

Prosecutors in Braunschweig said Monday that the investigation would concentrate on the suspicion of fraud committed through the sale of vehicles with manipulated emissions data.

It added that the probe aims to establish who was responsible. Prosecutors have received a number of criminal complaints in the case, including one from Volkswagen itself that doesn't name any suspects.

Under German law, it is not possible to bring charges against a company, only against individuals.

with files from The Associated Press